Gateway 386/33 User Manual page 129

Note: If you are occasion-
ally running out of memory
for the display list, you are
probably running out of
memory more often for the
fast redraw list, slowing
performance. If so, buying
one or two megabytes of
RAM greatly improves your
AutoCAD productivity. We
recommend that you pur-
chase expanded memory,
or extended memory and
an EMS emulator program.
Video Display and Display Adapter 9-33
drawings may require several megabytes. Display lists
for a drawing may be anywhere from one tenth the size
of the drawing file to three times the size; in general, the
display list averages about the same as the DWG file size.
The fast redraw list also occupies some memory, with the
worst case being that it occupies as much as the display
list. This means that you should count on both lists
generally taking up as much as twice the DWG file size.
Also, complex objects such as circles and text "expand"
when translated into display list format, so a drawing
witha lot of complex objects and text has a larger display
list than a simpler drawing.
In most cases, the memory you set aside for the display
list driver does not affect the underlying performance of
AutoCAD significantly. AutoCAD uses paging to sup-
port drawings larger than the amount of available
memory. Setting AutoCAD memory too low makes the
program swap pages more often, which leads to a
visible increase in disk activity. This activity generally
only occurs during a REGEN, which recreates the dis-
play list and causes the drawing file to be accessed
directly.
The AutoCAD manuals have an excellent section on
performance, concentrating on memory usage. To get
the most performance out of the program, read the
appropriate sections of those manuals as well as this
one.
What happens when the lists grow beyond the amount
of memory you set aside? If you have enabled an over-
flow drive for the display list, the list simply expands out
to disk. Otherwise, when the driver first runs out of
memory, it abandons the fast redraw list, slowing re-
draws to the speed of the fast zooms. Butif the display list
continues to grow until it, too, runs out of memory, it is
also abandoned, slowing all screen updates. Drawing
speed then reverts to AutoCAD standard speed.